314 EFFECT OF CHEMICAL AGENTS [Ch. XI 



(Raxjlin, '69). Embryos of various marine animals also will 

 not develop in tlie absence of phosphorus (Heebst, '97). The 

 peculiar importance of phosphorus for growth is also indicated 

 by the fact that Haetig and Webee ('88) found more phos- 

 phoric acid in the ash of the growing ends of the plant than in 

 its fully differentiated parts. Again, LoEW ('91^) found that 

 Spirogyra kept in a nutritive solution of salts in which phos- 

 phorus alone was lacking, continued to live and, indeed, to 

 form starch and albumen, but its cells did not grow or divide ; 

 so that LoEW concludes that an important use of phosphorus 

 is to nourish the cell-nucleus, and this fact is easily understood 

 from the known importance of the phosphorus-containing 

 nuclein of chromatin in cell-division. All these facts go to 

 show that phosphorus is of prime importance in the growth of 

 organisms. 



Arsenic, Antimony, Boron, and Bismuth, and their compounds, 

 are apparently all injurious to organisms, so that sublethal 

 solutions strong enough to be active, interfere with or even 

 inhibit growth. 



Sulphur. — This element is, without doubt, of constant oc- ■ 

 currence in organisms of all sorts, for it constitutes between 

 0.3% and 2% of all proteids, out of which organic bodies are 

 largely composed. Sulphur forms between 0.6% and 1% of 

 various (dry) organs of man, and nearly 1% of the dry sub- 

 stance of a month-old seedling of Sinapis alba. 



In the growth of a plant (Sinapis alba) the amount of its 

 sulphur increases from 0.02 mg. in the seed to 84.4 mg. in the 

 adult plant, and, indeed, it has been shown in one case 

 (Aebndt, '59, for the oat plant) that the percentage of sul- 

 phuric acid in the ash increases from 2.9 to 4.2 as the plant 

 develops from a seedling to maturity. Since the sulphur goes 

 chiefly into the composition of the living substance, its hylo- 

 genic importance for growth is evident. 



The form in which sulphur may be taken into the body is 

 very varied. It is well known that green plants usually 

 absorb it in the form of sulphates, especially sulphates of 

 potassium, calcium, and magnesium ; marine animals take it 

 chiefly from the calcic sulphate of sea water, and land animals 

 gain it largely from organic sulphur compounds produced in 



